The fundamental problem with many of the policies proposed under the rubric of social conservativism is that they are radically antithetical to the fundamental principles of individual liberty and freedom that are supposed to undergird conservativism in general.
To put it bluntly, the policies social conservatives wish to enact with respect to abortion are about as statist and controlling as a lot of democrat/socialist policies are, such as Obamacare. This is particularly so at the federal level: conservatives insist, in the abstract, that the federal government be cut back to the limited range of powers they believe the Constitution gives to the federal government - based on a fairly narrow reading of the Constitution - but when it comes to concrete policies social conservatives throw that belief out the window. There is nothing in the Constitution that authorizes the federal government to get involved in social issues like abortion. Period. End of discussion. And yet social conservatives consistently want to use the power of the federal government to prohibit abortion.
One cannot have one's cake and eat it, too; social conservatives can either have a limited federal government that exercises only those powers enumerated in the Constitution, or they can have an unlimited federal government that exercises whatever powers the party in power wishes to exercise, without regard to what the Constitution says. They cannot have both. If social conservatives really do believe in the former - that the federal government is limited - then they must accept the fact that they cannot use the power of the federal government to prohibit abortion; if social conservatives belief the latter - that they can have the federal government ban abortion notwithstanding the Constitution - then they are no better than the democrats/liberals whom they criticize for ignoring the limits on the federal government and enacting a comprehensive federal regime of social engineering.
That is the policy level of discussion; it's fairly academic, but it does expose the essential hypocrisy of social conservatives when it comes to issues like abortion. Millenials appear to be becoming disenchanted with the hypocrisy of the democrats/liberals, so it beggars the imagination why anyone would think they'd be attracted by another equally hypocritical social regime.
At the practical, real life, level, most younger women (of my generation and younger) - as has been explained to me by my wife, in no uncertain terms - do not see abortion as a desirable thing, as something to do on a whim, but neither do they want to feel trapped by the fear that if, for some unforseen, godforsaken, reason they should become pregnant, such as by being raped - which would include being sexually abused by a family member - they would have no other alternative than resorting to the sort of dirty backroom abortions that were the only sort available to most women prior to Roe v. Wade. It is the sort of existential fear that is not completely rational but which cuts to the core nonetheless. It is for that reason, and for many women that reason alone, that they do not want abortion to be eliminated. As such, they will not support someone who constantly threatens to ban abortion, even if they would otherwise agree with that same person on many other issues. Existential fears can be like that; they must be assuaged before anything else can be considered.
With respect to younger men, the existential fear isn't there - getting pregnant just isn't an option for men - but they do have an interest in responding to the fears of women, and at least some of them can empathize because they too have existential fears.
Social conservatives' constant threats to prohibit abortion - both at the federal and/or the state level - trigger that existential fear and thus chase off a lot of women - and men - who might otherwise agree with them on a range of other issues.
This is not to say that social conservatives should simply shut up and pretend that they don't care about abortion anymore; they shouldn't. However, it does mean that they should stop trying to use the wrong tools - the punitive, coercive, violent force of the government - to address abortion and should start finding better tools, such trying to convince others that abortion is wrong and to be avoided at all costs solely through the power of persuasion - of testifying to The Truth, if you will. In other words, private action, not government action, is more likely to constructively address abortion. After all, if you've managed to persuade everyone that abortion is wrong, then there is no need to have any laws that prohibit abortion.
Until social conservatives can come to terms with these two basic facts - at the least - they will continue to marginalize themselves and, by extension, the GOP.
A similar argument applies to the strident, sometimes xenophobic, views of many social conservatives on immigration.
